1. Field of the Invention
The present invention relates to a linear encoder for performing positional detection of relative motion that is used in mechanisms that perform said relative motion such as, for example, machine tools and industrial robots, and to a guide unit formed by adding a guiding device, having a track rail and so forth, that guides said relative motion, to said linear encoder.
2. Description of the Prior Art
An example of an apparatus of the prior art containing this type of guide unit is the direct drive unit indicated in FIG. 1. In contrast to a guide unit comprising the above-mentioned linear encoder and guiding device, this direct drive unit is provided with, for example, a linear motor for the driving device.
As indicated in FIG. 1, said direct drive unit has two track rails 2 that are mounted in parallel on base 1 and in which tracks are formed in the lengthwise direction in each to serve as a guiding device, and a slider 4 that is straddled across both said track rails 2 and guided by said tracks. In addition, a linear motor has a primary side (not shown) and a secondary side 6. Said primary side is composed of mutually connected permanent magnets and electromagnets and attached to the bottom surface of said slider 4. The secondary side 6 is composed of rectangular members wherein a plurality of inductor teeth (reference numeral not shown), having high magnetic permeability, are formed so as to be arranged in a row in the direction of the tracks. These inductor teeth and the magnetic poles of the above-mentioned electromagnets are arranged relative to each other.
On the other hand, a linear encoder is arranged on base 1 along one of track rails 2. Said linear encoder has a detected element in the form of a multipolar magnetized, long permanent magnet 8, wherein magnetic poles (N and S) are arranged in alternating fashion in a direction parallel to the tracks of said track rails 2, and an electromagnetic conversion element (not shown) in the form of a detecting element mounted on the bottom surface of the side of slider 4 so as to oppose said permanent magnet 8. The current position of slider 4 can be detected from the output of said electromagnetic conversion element that moves together with said slider 4 so as to travel longitudinally along permanent magnet 8.
Furthermore, reference number 9 in FIG. 1 indicates a cable guide housing a connection cable (not shown) for supplying a power source to the above-mentioned primary side of the linear motor, as well as for obtaining the output generated by the above-mentioned electromagnetic conversion element. As indicated in this figure, this cable guide 9 is composed of a plurality of links coupled in a row so as to be able to mutually pivot freely. Together with being formed so that said connection cable maintains a prescribed curvature even during movement of slider 4, it also serves to protect said connection cable from damage.
In the linear encoder equipped on the above-mentioned direct drive unit, since an electromagnetic conversion element is arranged on slider 4, the connection cable for obtaining the output signals from said electromagnetic conversion element must be arranged so as to be pulled around the entire moving range of slider 4. Moreover, cable guide 9 and so forth are also required which together with making the constitution complex, has the shortcoming of hindering smooth operation on the moving side, including slider 4, by the above-mentioned connection cable and cable guide 9.
In addition, since permanent magnet 8 equipped on the above-mentioned linear encoder is of a long shape, there is the additional shortcoming of the entire apparatus in which said linear encoder is incorporated being large in size.